Optical objective



asu-wc SR march OR 29-43-Qs`150n# N0'. 4, 1947. A, wARMlsl-{AM 2,430,150

oPrIcAL onJnc-Ivs I Filed septum.. 1943 3 sheets-sneu 1 'Rf R2 .R4-259% Rrns R9 m0 T20-5% D5 Inventor 0125 WTC |1004 NGV. 4, 1947. A, WARM|5HAM 2,430,150

OPTICAL OBJECTIVE Filed Sept. 27. 1943 3 Sheets-Sheet 3 Rl R2 R3 R4 R5 R6 R7 R8 R9 +O7.' 64 +-l745+i4243 7/66l P0 --07/86-44243-174/ 6 0l Sl D S D. $3 04 S4 D -Ol289 O 034g/ '003323 '0350/ '00598 O 012%9 D S D S D S4 Inventor O257 Ol Oo40 03?84 00% 037%4 '00140 O 'O 7 By Wir/71Min,

BGHR?" nuum Patented Nov. 4, 1947 UNITED STATES PATENT OFFICE Arthur Warmisham, Leicester, England, assignor to Taylor, Taylor & Hobson Limited, Leicester, England, a company of Great Britain Application September 27, 1943, Serial No. 503,974 In Great Britain August 25, 1942 22 Claims. (Cl. 88-57) l 2 This invention relates to an optical objective, for the D-line and the Abb V number of the corrected for spherical and chromatic aberramaterial of which each element is made. tions, coma, astigmatism and distortion, and intended more especially for use as a process ob- Example I jective, comprising two parts arranged approxi 5 [Equiva1enrfoca11engeh-995] mately holosymmetrically (that is with the two parts geometrically similar but not necessarily Thickness o, Re,rac Abbv identical in scale disposed on opposite sides of a Radius Air s eparative Number stop position from which they are axially spaced o Index "D at distances bearing the same ratio as the sizes l0 of the parts), the two parts usually consisting of R+Q930 Dl .01255 1.615 51,1 equal halves arranged symmetrically with respect Rai-1986 S 00 to the stop position to give copying at unit R, 3673 magnjcation, R 08746 Dg .00551 1.613 44.0

In the objective according to the present ini+. s, 01284 vention the two parts, each consisting of refract- R# D 00300 1 613 58 5 ing elements, are individually corrected for R, z=32,0+highreven powe'rs ofy astigmatism with respect to the stop position, R 08746 S 01469 whilst spherical aberration is corrected by means 1 D4 .00551 1.013 44.0 of a substantially afocal correcting surface R--3673 S 00 located substantially at the stop position. Ril-.198s

The correcting surface may be paraxially R 09930 D* -01256 M15 51'1 10'-- aiocal, 1n which case it will consist of a surface of revolution generated by rotation about the :iz-axis (that is the optical axis of the objective) Example H 0f a Curve 0f the fOlm [Equivalent focal length 1.000]

0::A 4 hi her owers f h y g p o y Thickness or Reirac- Abbv wherein the coeiiicients A are such that the Radius Air sepamtive Number surface will correct for the spherical aberration on Index "D of the refracting components. It may sometimes be preferable, however, instead of using a R+'09718 Dl 01098 1 615 5M paraxially afocal surface, to make the surface Ri+2248 afocal for a selected zone such that the chromatic Rahn?, S 00 difference of spherical aberration is reduced to a D: -00549 1.613 44-0 minimum. This necessitates that the surface R+'8719 s, 0374 shall have slight curvature at its axial point, and Ri D 003 1 613 58 5 the equation of the generating curve will become R, 1:22170 ;-nisghr even powers of.

=1/2y2|-Ay4+ higher powers of y ley-.08179 s '03926 b 40 RP 1727 D. .00549 1.013 44.0 wherein b is a constant large in comparison with M1248 S 'U0 the equivalent focal length of the objective. For Ds -01098 1615 550 such a surface to bensubstantialli afocal for a R '0918- slected zone of 7i, thv ,euguantiwtiedsmg and h should 45 mm 5y the equatin b=-1/(4Ah,2). It will be noticed that each of these examples Figures 1 to 9 of the accompanying drawings is exactly symmetrical about the stop position at respectively illustrate nine convenient practical which the afocal correcting Surface Re is diS- examples of objective according to the invention, posed, except only that the airgaD S2 iS leSS than and numerical data for such examples are given the argap S3 by an amOllrlt equal to the air in the following tables, in which RiRg equivalent of the thickness of the plate bearing represent the radii of curvature of the individual the correcting Surface. surfaces, the positive sign indicating that the In each example, all four lens components are surface is convex to the front and the negative simple and of meniscus shape with their concave that it is concave thereto, DiDz represent faces turned towards the stop position, the outer the axial thicknesses of the individual elements, components being convergent and the inner and S152 the axial lengths of the air spaces components divergent. between the components, the equation to the gen- In both cases the two halves are individually erating curve being given for the afocal correctcorrected for astigmatism with respect to the stop ing surface instead of its radius of curvature. 6o position, and the coma and distortion balance out The tables also give the mean refractive index owing to the symmetrical arrangement, whilst the curvature of the surfaces are so chosen as to give a substantially dat field. The examples are also corrected for chromatic aberrations. The residual spherical aberration of the two halves is substantially balanced out by that due to the deformation from the true plane surface of the afocal correcting surface, which owing to its location at the stop position does not materially interfere with the correction of the other aberrations.

The two examples are primarily intended as process objectives for copyingat or near unit magnification but can readily be modified to suit other magnifications, for which it will often be desirable to depart from a symmetrical arrangement of the two equal halves and to arrange the parts to be approximately geometrically similar to one another but of different sizes. Numerical data for one such example designed for a magnication of one half are given in the following table.

The above examples each employ a paraxially afocal correcting surface, but as mentioned above it will sometimes be preferable in practice to make the surfaceafocal for a selected zone such as to reduce the chromatic dierence of spherical aber ration to a minimum. Numerical data for one such example are given in the following table. v

In this'example the correcting surface is slightly concave to the front at the axis (the radius of curvature at the axial point being 11.387 times the equivalent focal length) and is made afocal for a zone of radius .032, the full radius of the stop being 0.48.

The above examples all employ simple components throughout but the invention is equally applicable to objectives in which the two divergent inner components are compound, and the following is an example of such an arrangement affording the highest aperture at present available for a copying objective.

Example V [Equivalent focal length 1.000. Relative Aperture F/2.8]

Thickness or Refrac- Radius Air Separative Abb V tion Index 14D Number Sx .0120 .RH-.3877

Dz 0923 1. 6133 59. 3 R4 S: .0930 Rs m D4 .0200 l. 6133 59. 3 R1 I=. 33201 4|higher even powers of D5 0388 1. 5795 40. 4 Rn 0 D5 0923 1. 6133 59.3 Rm. 3877 The foregoing examples employ optical glass throughout for the elements of the objective, but improved results can be obtained in many instances by employing crystalline materials for some or all of the elements. Crystalline alkaline halides and crystalline alums are especially suitable for the purpose. The remaining four examples all employ at least one such crystal in each part of the objective.

In this example, wherein the back focal length is .8972 times the equivalent focal length of the objective, the four components are all simple and the divergent two inner components are made of crystalline potassium bromide, dense barium crown glass being used for the convergent outer components. This example gives especially good correction for the chromatic aberu rations.

In this example, whose back focal length is .9207 times the equivalent focal length of the objective, the components are all simple. The convergent outer components are each made of crystalline potash selenium alum, whose chemical formula is KAl(SeO4)2.12H2O, whilst the divergent inner components are made of crystalline thallium iron alum, TlFe(SO4)2.12H2O.

Example VIII [Equivalent local length 1.000]

Thickness or Refrac- Abb V Radius Air Separative tion Index 1m N umher Si R3+. 16006 Dz 00598 1. 7876 23. 9 R4+. 08852 Sz 03401 Rs N D3 .00323 1. 613 59. 3 Re z=23. 521J+higher even Powers of Sa 03601 R1-. 08852 D4 .00598 1. 7876 23. 9 Rs-. 16006 S4 0 Re 22130 Ds 01289 1. 712 29. 7 Rm. 10018 This example, whose back focal length is .9444 times the equivalent focal length of the objective, differs from Example VII in using alkaline halide crystals instead of alum crystals, the divergent inner components being made of caesium iodide crystal and the convergent outer components of ammonium bromide crystal.

Example IX [Equivalent local length 1.000]

Thickness or Refrac Abb V Radius A11l Separative tion Index 'np Number Dz 00440 1.6984 34. 6 Rri. 06709 Ds 00323 1. 613 59. 3 R4 z=259. 2114+higher even powers of D4 00440 1. 6984 34. 6 Rs. 14565 This example, whose back focal length is .9221 times the equivalent focal length of the objective, employs an alkaline halide crystal, caesium bromide, for the divergent inner components and an alum crystal, potash iron alum for the convergent outer components.

By holosymmetrical or holosymmetrically" in the claims is meant a symmetrical system composed of two symmetrical parts which may or may not be of the same size and in which the dimensions of the components of each part are in a xed ratio to the corresponding components of the other part.

What I claim as my invention and desire to secure by Letters Patent is:

1. An optical objective, comprising two parts each consisting of a convergent refracting component and a divergent refracting component, ,the two parts being arranged approximately holosymmetrically and the innermost and outermost radii being between 4.3 and 15.4 per cent of the equivalent focal length, the dimensions of one part being derived from the dimensions of onehalf of an equivalent objective comprising two equal halves by multiplying said last named dimensions by a factor not less than 1.0 and not greater than 2.0 and the dimensions of the other part being derived by dividing said dimensions of one-half of said equivalent objective by the same factor, said two parts being individually corrected for astigmatism with respect to .the stop position, and a substantially afocal correcting surface located substantially at the stop position for correcting for the spherical aberration of the objective, the objective also being corrected for chromatic aberrations, coma and distortion.

2. An optical objective as claimed in claim l, in which the four components are all meniscusshaped with their concave surfaces facing the stop position.

3. An optical objective as claimed in claim 1, in which at least one of the elements in each part of the objective is made of an alkaline halide crystal.

4. An optical objective as claimed in claim 1, in which at least one of the elements in each part of the objective is made of a crystalline alum.

5. An optical objective as claimed in claim 1, in

which the afocal correcting surface consists of a surface of revolution generated by rotation about the :r-axis of a curve of the form wherein the coefficients A are such that the surface will correct for the spherical aberration of the refracting components wherein :r and y are the Iparameters of a system of Cartesian coordinates whose x-axis coincides with the optical axis of the objective.

6. An optical objective as claimed in claim l, in which the afocal correcting surface consists of a surface of revolution generated by rotation about the :r-axis of a curve of the form wherein bis a constant large in comparison with the equivalent focal length of the objective and the coefficients A are such that the surface will correct for the spherical aberration of the refractlng components, wherein a: and y are the meditoparameters of a system of Cartesian coordinates whose x-axis coincides with the optical axis of the objective.

7. An optical objective, comprising two equal halves disposed symmetrically about a stop position, the two halves each consisting of a convergent refracting component and a divergent refracting component; and being individually corrected for astigmatism with respect to the stop position, the innermost and outermost radii being between six and eleven percent of the equivalent focal length and a substantially afocal correcting surface located substantially at the stop position for correcting for the spherical aberration of the objective, the objective also being corrected for chromatic aberrations, coma and distortion.

8. An optical objective as claimed in claim 7, in which the afocal correcting surface consists of a surface of revolution generated by rotation about the :1t-axis of a curve of the form a:=Ay4+. higher powers of y wherein the coeilicients A. are such that the surface will correct for the spherical aberration of the refracting components, wherein a: and y are the parameters of a system of Cartesian coordinates whose .'c-axis coincides with the optical axis of the objective.

9. An optical objective as claimed in claim 7, in which the afocal correcting surface consists of a surface of revolution generated by rotation about the .1:-axis of a curve of the form wherein b is a constant large in comparison with the equivalent focal length of the objective and the coefficients A. are such that the surface will correct for the spherical aberration of the refracting components wherein :c and y are the parameters of a system of Cartesian coordinates whose :c-axis coincides with the optical axis of 4the objective.

10. A holosymmetrical modification of the optical objective as claimed in claim 'l derived therefrom by multiplying the dimensions of one half of said objective by a factor greater than 1.0 and not greater than 2.0 and dividing the dimensions of the other half of said objective by the same factor.

11. An optical objective, comprising four simple meniscus components disposed symmetrically with their concave surfaces facing the stopr position, the two outer components being convergent and the two inner components divergent, the two halves being individually corrected for astigmatism with respect to the stop position, the innermost and outermost radii being between six and eleven .percent of the equivalent focal length and a substantially afocal correcting surface located substantially at the stop position for correcting for the spherical aberration of the objective, the objective also being corrected for chromatic aberrations, coma and distortion.

12. An optical objective as claimed in claim 11, in which at least one of the elements in each half of the objective is made of an alkaline halide crystal.

13. An optical objective as claimed in claim 11, in which at least one of the elements in each half of the objective is made of a crystalline alum.

8 14. An optical objective as claimed in claim 1l, in which the afocal correcting surface consists of a surface of revolution generated by rotationl about the x-axis of a curve of the form x=Ay4| higher powers of y wherein the coefficients A are such that the surface will correct for the spherical aberration of the refracting components wherein :z: and y are the parameters of a system of Cartesian coordinates whose -axis coincides with the optical axis of the objective.

15. An optical objective as claimed in claim 11, in which the afocal correcting surface consists of a surface of revolution generated by rotation about the :zz-axis of a curve of the form 2 x=+fly4+ higher powers ofy wherein b is a constant large in comparison with the equivalent focal length of the objective and the coefficients A are such that the surface will correct for the spherical aberration of the refracting components wherein :c and y are the parameters of a system of Cartesian coordinates whose z-axs coincides with the optical axis of the objective.

16. An optical objective as claimed in claim 11, in which the radius of curvature of each of the two outermost surfaces of the objective lies between .09 and .11 times the equivalent focal length of the objective, and the radius of curvature of each of the two innermost surfaces of the objectives lies between .08 and .10 times such equivalent focal length.

1'7. An optical objective as claimed in claim ll, in which the two divergent components are made of an alkaline halide crystal and the two convergent components of a crystalline alum, the radii of curvature of the two outermost surfaces and of the two innermost surfaces all lying between .06 and .O7 times the equivalent focal length of the objective.

18. An optical objective as claimed in claim 11, in which the radii of -curvature of the two outermost surfaces and of the two innermost surfaces of the objective all lie between .06 and .07 times the equivalent focal length of the objective.

19. An opticalobjective, comprising four meniscus components disposed symmetrically with their concave surfaces facing the stop position, the two outer components being simple and convergent whilst the two inner components are cornpound and divergent, the outermost radii of curvature of said outer components lying between fifty and sixty percent and the innermost radii of curvature of said inner components lying between twenty and thirty percent and the outer radii of curvature of said inner components lying between thirty and forty percent of the equivalent focal length of said objective, the two halves being individually corrected for astigmatism with respect to the stop position, and a substantially afocal correcting surface located substantially at the stop position for correcting for the spherical aberration of the objective, the objective also being corrected for chromatic aberrations, coma and distortion.

20. An optical objective having numerical data substantially as set forth in the following table:

Search Roo [Equivalent focal length 1.000]

Thickness or Refrac- Abb V Radius Air Separative tion Index 1in Number Di .01152 1. 615 55.0 Rz-i. 23268 Dz 00576 1. 613 44. R4+. 09141 Si 03724 Rs e D: .00576 l. 615 55.0 Rt :c= 0438u2+2L 50i/+hi gher even powers of y.

Si 04108 R1-. 09141 D4 .00576 1. 613 44. 0 Rs. 18107 Ds 01152 l. 615 55.0 R1u. 10135 wherein RiRz represent the radii of curvature of the individual surfaces, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, D1D2 represent the axial thickness of the individual elements, and SlSz the axial lengths of the air spaces between the components, the equation to the generating curve being given for the afocal correcting surface and wherein :c and y are the parameters of a system of Cartesian coordinates whose avt-axis coincides with the optical axis of the objective.

21. An optical objective having numerical data substantially as set forth in the following table:

wherein RiRz represent the radii of curvature of the individual surfaces, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, D1D2 represent the axial thickness of the individual elements, and SiSz the axial lengths of the air spaces between the components, the equation to the generating curve being given for the afocal correcting surface and wherein a: and y are the parameters of a system of Cartesian coordinates whose :it-axis coincides with the optical axis of the objective.

22. An optical objective having numerical data. substantially as set Iforth in the following table:

[Equivalent focal length 1.000]

Thickness or Refrac- Radius Air Separative Abb V tion Index 'nn Number D; .02657 1. 4817 40.7 Rz+. 24052 S1 0 Rai-.14565 Sz .03584 R5 D; .00323 1.613 59.3 Rg z=259. 2u4+higher even powers o! u.

Di .00440 1.6984 34.6 Ri. 14565 wherein RrRz represent the radii of curvature of the individual surfaces, the positive sign indicating that the surface is convex to the front and the negative sign that it is concave thereto, DiDz represent the axial thickness of the individual elements, and SiSz the axial lengths of the air spaces between the components, the equation to the generating curve being given for the afocal correcting surface and wherein a: and y are the parameters of a system of Cartesian coordinates whose -axis coincides with the optical axis of the objective.

ARTHUR WARMISHAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 583,336 Rudolph May 25, 1897 871,559 Beck et al Nov. 19, 1907 1,541,407 Spannenberg June 9, 1925 2,100,290 Lee Nov. 23, 1937 2,170,979 Straubel Aug. 29, 1939 2,332,930 Rinia Oct. 26, 1943 2,336,207 Aklin Dec. 7, 1943 FOREIGN PATENTS Number Country Date 10,131 Great Britain 1893 14,673 Great Britain 1908 537,460 France March 3, 1922 548,384 Great Britain Oct. 8. 1942 

